We wish to learn how visual excitation and adaptation takes place and the nature of the initial events in the visual process. We plan to study the structure of the chromophore of rhodopsin, the spectrum of rhodopsin, the structure of the membrane of the rod outer segment, the biophysical and biochemical properties of the proteins which compose it, and the mechanism of permeability control. We have become especially interested in the role of cyclic nucleotides in the visual system. We feel that this research will prove significant not only to understanding of the visual system, but also to our knowledge of the excitable membranes of all sensory systems.